Parachutes have evolved over the years into highly sophisticated systems, and include features that improve the safety, maneuverability, and overall reliability of the parachutes. A ram-air canopy or gliding ram air parachute is a form of a self-inflating “ram-air” canopy or airfoil, also know as a parafoil. Such ram air canopies improve the control of speed and direction of parachute type devices.
The U.S. Army Defense Department makes use of airdrop for troop resupply and humanitarian aid. Aircraft vulnerability requires the deployment of gliding ram air parachutes to offset the aircraft at a safe distance and altitude. Once these ram air canopies are open, they are able to glide to the targeted “drop zone” using guidance systems that are GPS controlled. Improving the glide ratio of the ram air canopy provides aircraft commanders with more options and improves aircraft survivability. Increased glide can also offer larger payload capabilities.
The ram air canopy parachute, generally referred to as a ram air canopy, is formed of two layers of material, often referred to as a top skin and a bottom skin. The skins or layers may have different shapes but are commonly rectangular or elliptical. The top and bottom layers are connected by airfoil-shaped, vertically oriented, fabric ribs to form cells. The cells fill with high pressure air from vents that face forward on the leading edge of the airfoil. The fabric is shaped and the parachute lines trimmed under load such that the ballooning fabric inflates into an airfoil shape
The canopy of the ram air parachute functions as a wing to provide lift and forward motion. Guide lines operated by a parachutist allows for the deformation of the canopy to control direction and speed. Ram air parachutes have a high degree of maneuverability.
FIGS. 1 and 2 illustrate aspects of a typical ram air canopy 100. FIG. 1 illustrates a spanwise inflated ram air canopy 100. FIG. 2 is the inflated spanwise view of a ram air wing 110 of the ram air canopy 100, looking into an open leading edge 102 of the ram air wing 110.
Two-dimensional numerical simulations of the airflow around ram air canopies, such as the ram air canopy 100 of FIG. 2, have shown a region 120 of separated flow on the lower lip 104 of the open leading edge 102. This region 120 of separated flow, also referred to as a region of low pressure, or flow separation bubble, is caused by the lower lip 104 or edge of the ram air wing 110. This flow separation bubble 120 is generally due to the inability of the flow of air to negotiate the sharp turn at the lower lip or edge 104. Low pressure areas, such as region 120 attached to the lower surface or lip 104 of an airfoil 110, are generally detrimental to the glide ratio.
As is shown in the example of FIG. 2, a vortex 106 forms on an inside of the canopy wing 110, just inside the open leading edge 102. This vortex 106 directs the flow of air toward the lower lip 104 during steady flight, and the opening 108 in the leading edge 102 makes the ram air wing 110 less aerodynamic. In the illustration of FIG. 1, looking into the open leading edges 102 of the ram air canopy 100, the area of separation 120 is shown along the span of the lower canopy surface 112. This flow separation region 120 is quite large when viewed three-dimensionally and produces a large reduction in glide ratio. It would be advantageous to reduce or eliminate the leading edge separation bubble in order to improve the aerodynamic efficiency of a ram air canopy.
There have been various attempts to improve glide capability of ram air canopies by various means. A good example is adding inflatable bladders into the canopy cells. This method adds stiffness to the ram air canopy and provides a leading edge that resembles a rounded wing geometry. This approach has been shown to result in increased performance. However, this method adds complexity to the ram air canopy system with additional hardware for pressure inflation.
Accordingly, it would be desirable to provide a ram air canopy that addresses at least some of the problems identified above.